Spinal implants such as spinal interbody fusion devices are used to treat degenerative disc disease and other damages or defects in the spinal disc between adjacent vertebrae. The disc may be herniated or suffering from a variety of degenerative conditions, such that the anatomical function of the spinal disc is disrupted. Most prevalent surgical treatment for these conditions is to fuse the two vertebrae surrounding the affected disc. In most cases, the entire disc will be removed, except for a portion of the annulus, by way of a discectomy procedure. A spinal fusion device is then introduced into the intradiscal space and suitable bone graft or bone substitute material is placed substantially in and/or adjacent the device in order to promote fusion between two adjacent vertebrae.
There are various approaches that a surgeon may take to perform spinal fusion. Such approaches include a posterior approach, which is accessed from the back of the spine, or an anterior approach, which is accessed from the front. Other approaches which may be used include a transforaminal approach and a lateral approach, which is accessed from the side of the patient. The particular approach selected is primarily determined by the type of treatment to be administered by the surgeon. For patients that require treatment for conditions including degenerative disc disease, spinal instability or deformity, anterior lumbar interbody fusion (ALIF) has been found to be effective. The ALIF procedure and associated devices have certain advantages over other procedures. The first is that there is typically less disruption to surrounding musculature and nerves. Once access is achieved, there is a relatively open space to work in. This allows for more efficient removal of disc material thereby providing a larger potential fusion bed. The ALIF procedure also allows for a larger implant both in footprint and height, which creates better height and lordosis restoration as well as greater spinal stability.
Anterior lumbar interbody fusion requires an incision through the patient's abdomen and retraction of the surrounding muscles and abdominal contents to the side. After the affected disc is removed a structural ALIF device or implant is inserted which may be packed before, during or after insertion with a suitable bone graft material. Some types of ALIF devices are expandable so as to correct height between adjacent vertebrae. In certain of these expandable ALIF devices only the anterior end is specifically expandable, so as to produce an expansion of the disc height at the anterior side greater than the posterior side in an effort to correct lordosis. Examples of such expandable devices include U.S. Pat. No. 6,773,460, issued to Roger P. Jackson on Aug. 10, 2004, and U.S. Pat. No. 6,102,950, issued to Alex Vacarro on Aug. 15, 2000. While it is typically not desirable to increase the posterior side greater than the anterior side, it is often desirable to increase both the posterior and anterior sides an amount sufficient to not only correct disc height but to also adequately decompress neural elements.
Furthermore, it is desirable that an expandable ALIF device allow for maximum introduction of biologic bone graft material as well as for optimized openings in the inferior and superior surfaces of the ALIF device so as to maximize contact area between graft material and the endplates of the opposing vertebral bodies. Certain of the known expandable ALIF devices include expansion structure or mechanisms that tend to impede the graft loading process, particularly after expansion.
Accordingly, there is a need for an improved expandable ALIF fusion device to address these shortcomings.